Hair treatment (conditioning, reshaping, relaxing and dyeing of human hair) is a substantial part of the cosmetic and beautician industry. Huge sums of money are spent on products and services in salons and in the home.
There exists a vast array of compositions for those purposes, many of them harsh and difficult to use, requiring the skill of hairdressers, in order not to damage the hair.
In the context of conventional materials used for the reshaping of hair, commonly referred to as giving "a permanent," there are two broad classes. The first includes malodorous thio-alcohol/acid derivatives such as thioglycolic acid, thiopropionic acid, monothio-glycerol, etc. Treatment includes a rinse step with an appropriate oxidizer in a carefully controlled application.
The second general treatment involves the use of relatively strong caustic alkaline solutions formed from hydroxides of alkali and alkaline earth elements such as sodium hydroxide, calcium hydroxide, etc. With such treatment, it is necessary to further treat the hair with a neutralizing wash to obtain a physiologically compatible pH. It is known in the cosmetic industry that both of the above-specified treatments are harsh and may adversely affect the scalp or, if employed improperly, the hair itself. For example, the "neutralizing" step requires careful application in order to prevent exposure of the hair to too much or too little of the appropriate reagents.